The present invention generally relates to the polymerization of monomers in carbon dioxide to form water soluble polymers.
In recent years, carbon dioxide has been proposed an attractive solvent for the homogeneous polymerization of fluorinated monomers and heterogeneous processes such as dispersion polymerizations. It has an easily accessible critical point with a Tc of 31.1xc2x0 C. and a Pc of 73.8 bar. Within this region, supercritical CO2 exists as a low viscosity medium with tunable densities. Two classes of polymers have shown appreciable solubilities in supercritical CO2: amorphous fluoropolymers and silicones. Both classes of materials have been found to be efficient stabilizers in the dispersion polymerization of olefinic monomers in carbon dioxide. The dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide using a fluorinated polymeric surfactant, poly(1,1-dihydroperfluorooctyl acrylate) [poly(FOA)] has been proposed by DeSimone, J. et al., Science, 1994, 265, 356. These polymerizations yielded micrometer-sized particles with potentially narrow size distributions. After further investigation, this system was extended to include poly(dimethylsiloxane) [PDMS] which contained a polymerizable end group. The dispersion polymerization of styrene in carbon dioxide has also been proposed.
Limited research efforts have been reported on the dispersion polymerization of water soluble vinylic monomers in carbon dioxide. Adamsky and Beckman, Macromolecules, 1994, 27, 312-314 reported the inverse emulsion polymerization of acrylamide in supercritical CO2, but the dispersion process remains to be explored.
In one aspect, the invention provides a method of forming a water soluble polymer. The method comprises polymerizing a non-fluorinated monomer in a reaction medium comprising carbon dioxide to form a water soluble polymer. The polymerization is carried out in the presence of a surfactant that stabilizes the water soluble polymer in the reaction medium.
In another aspect, the invention provides a method of forming a water soluble polymer. The method comprises polymerizing a non-fluorinated monomer in a reaction medium comprising carbon dioxide to form a water soluble polymer, wherein the polymerization is carried out in the presence of a surfactant that stabilizes the water soluble polymer in the reaction medium. Thereafter, the reaction medium is separated from the water soluble polymer to isolate the water soluble polymer.
In another aspect, the invention provides a reaction mixture comprising a non-fluorinated monomer, a reaction medium comprising carbon dioxide, and a surfactant.
In another aspect, the invention provides a method of making a water soluble polymer. The method comprises polymerizing a non-fluorinated acrylamide-based monomer in the presence of an initiator in a reaction medium comprising carbon dioxide to form a water soluble polymer. The non-fluorinated monomer and initiator are solubilized in the carbon dioxide reaction medium and the polymerization is a precipitation polymerization.
In another aspect, the invention comprises a composition of matter.
The composition of matter comprises a non-fluorinated acrylamide-based monomer, an initiator, and a reaction medium comprising carbon dioxide. The non-fluorinated acrylamide-based monomer and initiator are solubilized in the reaction medium, and the non-fluorinated acrylamide-based monomer is capable of reacting to form a water soluble polymer which precipitates out of the reaction medium.
These and other aspects and advantages of the invention are set forth in detail hereinbelow.